Method of treating hides and skins



' Patented Mar. 14, 1944 METHOD OF TREATING HIDES AND SKINS Oliver William Robertson, Brookline, Mass., as-

signor to Continental Machinery 00., Inc., New Bedford, Mass., a corporation of Massachusetts No Drawing. Application July 16, 1942,

Serial No. 451,213 j 21 Claims.

The present invention relates to methods of treating hides and skins, including tanning and degreasing, and more particularly, hides and skins of high-fat content, such as hog. Pig, sheep, lamb and seal skins. The present application is a continuation-in-part of application Serial No. 368,256, filed December 2, 1940.

For many years, it was considered that, generally speaking, and with a minor exception hereinafter referred to, hides and skins of high-fat content should be degreased prior to tanning.-

Various reasons were advanced in support of this view; among them, that previous removal of the natural fats or greases of the hides and skins would'aid the tanning solutions to penetrate the fibres thereof more easily than when they are impregnated with fats and oils.

In accordance'with common prior-art methods, in which the degreasing precedes the tanning, however, the degreasing has not been sufficiently thorough. The natural greases and fats have not always been fully removed, particularly the stearines and other solid fats, and what has been left behind has not been uniformly distributed throughout the skins or hides. This has introduced spue into the finished leather, and has also marred the uniformity of the protective action of the natural oils and fats in the fibres, leaving dry boardy sections in a leather of non-uniform color, and consequently increasing the quantity of rejected leather. In some cases, indeed, it has been necessary to degrease a second time, after the tanning. It is uneconomical and otherwise undesirable, however, to degrease twice, and to sandwich a tanning operation in between the two degreasing operations.

There are great advantages in tanning the raw skins or hides before degreasing. First, the degreasing solvents have definite burning and other deleterious weakening effects upon the fibres of previously untanned hides or skins, leaving the leather fiat, soft and raggy. If the hides or skins are tanned prior to degreasing, however, the fibres thereof become encased in a protective coating of the tanning materials that resists the burning and other injurious action of the degreasing agents. Leather made from hides and skins that have been tanned prior to degreasing, therefore, is much more plump, and contains longer, stronger and tougher fibres that enables it better to resist abrasion and tearing.

When the skins or hides are tanned in the grease, followed by a proper subsequent degreasing, furthermore, the tanned fibres thu produced are almost entirely free of fats and oils. What residual fats remain behind are redistributed with substantial uniformity, and the fibres are substantially stronger for the further reason of the protective actwn of these uniformly re-distributed natural fat and oils.

There is no difliculty about tanning skins or hides of low-fat content, such as cow and horse hides, prior to degreasing. C ow and horse hides have so little natural fat and oil that it is not necessary to 'degrease themat all. The problem does, however, arise in connection with skins or hides of high-fat content that are highly impregnated with grease.

Tanning of light-weight and medium-weight sheep-skins before degreasing has been practiced heretofore to some extent, particularly for the production of certain kinds of light-colored leather. This has been with the aid of vegetable tanning extracts only. The skins so vegetabletanned have then been dried, after which they have been degreased in this dry state, with the aid of naphtha. Following upon this degreaslng, the leather has been finished in light colors. The drying of the skins prior to the degreasin was considered to be necessary because the agents employed for removing the grease from the skins could not penetrate the wet vegetabletanned fibres.

This method of vegetable tanning prior to degreasing has been regarded as an evil that, however, was unavoidable. It has been considered to be necessary to tan prior to degreasing, in these cases, because, with prior degreasing, sufficient residual fats and oils would have been left in the fibres of the skins or hides to produce a blotchy-appearing leather subsequent to the dyeing and the finishing.

A lower grade of leather, moreover, is produced when the skins are dried prior to removing their natural fats by degreasing. Any piece of leather that has been degreased in the dried state will yield weakened fibres. It lacks strength and toughness. Hides and skins that have been degreased in the wet, on the other hand, are quite resistant to abrasion and tearing.

The advantages that might otherwise havebeen obtained by the prior vegetable tanning of the prior art become thereby largely lost through the subsequent degreasing in the dry state.

It has not heretofore been possible to employ this method in connection with chromeor other mineral-tanning agents; or with heavy-weight sheepskins, however tanned. If chrome-tanned skins or hides are once dried prior to degreasing,

before they have received their proper fat liquor, a hard and boardy leather results that can never be re-wet to the same degree of suppleness as before the drying. This isnot true of vegetabletanned skins, which may be dried and re-wet a number of times.

According to the disclosure of the said application, the wet pickled, hides or skins of high-fat content are tanned whileistill containing their full natural-fat content.v 'The tanning is there,

described as effected with the aid of an emulsifier, which may be vegetable or mineral. The emulsifier produces an emulsion of the natural fats and oils of the skin with the tanning materials employed by acting as a surface-tension depressant for both the natural fats and oils and the liquids of both, the skin and the tanning effect this tanning. Sheepskins of light-fat and medium-fat content are still skins of high-fat content; they are to be distinguished from horse and cow hides, which are of very low-f at content.

The theory underlying this phenomenon. is obscure. It may tentatively be advanced, however, that, unlike degreasing agents, the tanning agents ordinarily employed, because they are aqueous solutions, and are therefore miscible with the water in the fibres of the wet skins or hides,

can penetrate the inner fibres of the skins or hides, to reach the fats and oils embedded in the fat cells thereof, to a reasonable degree, even in the absence of the emulsifier.

may be omitted in the case of skins or hides of high-fat content that are not too heavily laden otherwise not miscible with the grease, to penetrate the innermost grease-impregnated fibres of the skins or hides, so as to become miscible therewith.

An object of the present invention, accordingly,

is to provide a new and improved method of treating skins or hides of high-fat content.

A further object is to provide a novel method, according to which the skins or hides are tanned before any of the natural fats or oils are removed.

Another object is to tan skins or hides of highfat content with mineral-tanning agents prior to degreasing.

Still a further object is to provide an improved method according to which the tanned skins or hides are degreased in the wet.

A further object of the invention is to provide a new and improved method of treating lightweight and medium-weight skins of high-fat content, according to which the skins are tanned, after whichpthe tanned skins are degreased in the wet. The tanning may be effected with or without the aid of an emulsifying agent.

Other and further objects will be described hereinafter and will be particularly pointed out in the appended claims.

The following will serve as an illustration of a tanning solution suitable for tanning twenty-five dozen pickled sheepskins in the grease:

Salt water ll n 100 Chrome tan, such as tanolin supplied by R. Martin Dennis Co pounds 70 The fatty-alcohol sulphate or other emulsifier Whether or not an emulsifier is embodied in the tanning fluid, the fibres of the tanned undegreased skins or hides become thus protected with a coating of tan molecules that inhibit the harsh and astringent action of the solvent that is subsequently used in the degreasing process. This results in producing stronger fibres.

The skins or hides may be subjected to the action of this tanning solution in a suitable tanning chamber during a period of from 2 to 3 hours. After the still grease-laden hides or skins have thus been tanned, they are piled smoothly and permitted to lie undisturbed for They are then fleshed, to remove any a time. l'ong-fiesh fibres.-

The tanned fleshed hides or skins, while still in their wet state, are then introduced into a suitable closed air-,-tight machine, such as the machine disclosed in application Serial No. 389,633, filed April 18, 1941. They are taken in the wet state, without the necessity for drying them. A chlorinated hydrocarbon or other suitadded.

An aqueous chlorinated-hydrocarbon-water emulsion suitable for degreasing the 25 dozen tanned wet sheepskins may comprise gallons trichlorethylene, 50 gallons of water-which water may already be present in the wet tanned skins or hides, so that no additional water may be required-and 5 pounds of a fatty-alcoholsulphate emulsifier, such as Duponal-D paste.

The machine is thereupon set into operation to effect the degreasing oi' the skins or hides. The skins or hides become impregnated with the degreasing fiuid containing the emulsifier. The machine of the above-described application performs this operation by tumbling the hides o'r skins in the degreasing solvent. The machine may be operated for about ten minutes, the temperature in the air-tight chamber being maintained preferably at from about 60 degrees F. to 75 degrees F., though it may be higher. It should be sufficiently high to facilitate the degreasing of the skins or hides, but not so high as to injure them.

Though the theory is not fully understood, the probable explanation is that, when the degreasing of the hides or skins is effected in the wet state, the water present in the liquid-impregnated fibres thereof cushions the harmful effects that might otherwise be produced by the degreasing solvents on the fibres.

The emulsifier is needed during degreasing beable grease solvent and an emulsifier are then cause the solvents used for degreasing, unlike the tanning solutions, are not miscible with the water contained in the wet tanned skins or hides. The emulsifier, however, mixes with the solvents to produce an emulsion, thus enabling the degreasing agents to penetrate the aqueous solutions with which the wet fibres of the wet skins or hides are impregnated.

The hydrocarbon emulsion may be either of the oil-in-water type above described, or the water-in-oil type, in which the water phase is dispersed in the oil phase. The oil-in-water type of emulsifier is preferable for light-fatand medium-fat-content skins, and the water-in-oil for the heavy-fat-content skins. To produce an oil-in-water emulsion, a water-soluble emulsifier is first dissolved in water, the oil being added At the end of the ten-minute period, the solvent emulsion, with the fats and oils contained therein, is pumped or drained into a still", for the purpose of reclaiming both the. solvent and the fats and oils. The operation may be repeated in the case of heavy hides or skins.

Though the skins or hides have thus become separated or removed from theliquid of the degreasing bath, they still contain'a certain amount of residual solvents. The residual solvents thus still remaining in the skins or hides, after this de'greasing operation, may then be substantially completely removed by drying, preferably with the aid of a vacuum pump. This may be in the same machine in which the degreasing was eifected. The vacuum produces a rarefied pressure that serves to extract the residual solvents by distillation or boiling out.

This distillation of the residual solvents caused by the vacuum, however, results in rapidly cooling the skins or hides, due to the loss of latent heat of vaporization and other heat losses. At the resulting low temperatures, it would be impossible to remove the residual solvents.

With the machine still operating, therefore, additional heat may be supplied in the form of hot water or steam, or in any other desired way, to compensate for this cooling, during the extraction of the residual degreasing fluid, thus keeping the skins or hides warm during the extraction. One should be careful, however, not to supply so much heat as to injure the skins or hides, because an excess of heat would convert the collogen of the skins or hides into glue.

The tanning prior to the degreaslng, as described above, permits of accompanying the high vacuum with a temperature sufliciently high to enable the vacuum to effect the boiling off of the residual solvents, but not so high as to injure the skins or hides. tanning is effected prior to the degreasing, the collogen of the hides or skins becomes better fixed by the tanning materials. As a consequence of this fixing, the fibresof the skins or hides become resistant to higher temperatures.

This is because, when the The temperature, during the evacuation process,

vantages, among others.

point of methylene will stand up to degrees F. in the wet state, and somewhat higher, if dry. Where chrome tanning'is employed, the wet fibres will stand up to a temperature substantially as high as the boiling temperature of water, 212 degrees-F.

At these higher temperatures, moreover, the natural fats inthe tanned skins or hides become liquefied more quickly, which results in two ad- First, the natural fats become more easily extracted from the fibres of the skins or hides by the chlorinated-hydrocarbon or other emulsion; and secondly, the very small amounts of residual fats and oils still remaining in the skins or hides become more uniformly re-distributed therein.

The employment of these higher temperatures is particularly desirable in the case of light-' weight and medium-weight sheep-skins, and when the degreasing solvent employed is trichlorethylene or its equivalent. It has vbeen found, in practice, however, that trichlorethylene is not effective to degrease heavy-weight sheepskins at these. high temperatures, but is quite effective to perform the degreasing operation at lower temperatures, say, room temperature, or about '70 degrees F. No consistent theoretical explanations for these apparently paradoxical phenomena have yet been advanced. I

The vacuumdistillation of the solvent is particularlydesirable when the solvent has a boiling point above about degrees F. The vacuum distillation may not, however, be needed in other cases, as when methylene chloride is employed. In the case of methylenechloride and similar solvents, moreover, the temperature employed may be rather low, because the boiling chloride is about 103 degrees F.

At the end of about ten to fifteen minutes of vacuum distillation, the solvent will become substantially completely distilled out of the skins or hides, whereupon they may .be removed from the degreasing machine, and subjected -to the usual coloring and fat liquoring processes, and to the addition of oils, where needed, to make the fibres of the leather more flexible.

By thus tanning prior to degreasing, and then degreasing in the wet, a better, plumper, softer, tougher and more full-bodied leather, of finer quality, is obtained, with a full, smooth, round mellow feel to it, and this irrespective of whether the tanning agent is mineral or vegetable. A leather is produced the color of which is quite uniform, and without the grease spots found in many usual leathers. It stretches uniformly without breaks, and without producing looseness. 'Even the flesh or the inner side of the leather has a beautiful nap, missing from leathers made according to prior-art methods.

Among other oil-in-water fatty-alcohol-sulphate emulsifiers may be mentioned Duponol 80, the ulpate of octyl fatty alcohol, ,Alkanol W. X. N., sodium naphthalene sulphonic acid, and Emulphor O'.- Among the water-in-oil emulsifiers may be included sodium naphthanate and solvent-soluble Duponol O S, a mixture of the sulphate of oleyl alcohol and vunsulphonated oleyl alcohol.

Modifications will occur to persons skilled in the art and all such are considered to fall within the spirit and scope of the invention as defined in the appended claims. a What is claimed is: 1. The described process of treating skins o hides of high-fat content consisting inafirst tanning the hides or skins of high-fat content by subjecting them to the action of an aqueous tanning solution containing a fatty alcohol sulthe wet tanned skins by subjecting them to the.

action of an aqueous chlorinated hydrocarbon emulsion.

- 3. The described process of treating skins or hides of high-fat content consisting in first tanning the hides or skins of high-fat content by subjecting them to the action of an aqueous tanning solution containing a fatty alcohol sulfate as an emulsifier so as to tan the fibres and redistribute the resident natural fats and oils in protective relation to the fibres; then degreasing the wet'tan'ned skins by subjecting them to the action of an aqueous chlorinated hydrocarbon emulsion, and then extracting the resultant fluid fats and oils from the skins.

4. A method of treating skins or hides of high- 'fat content that comprises first tanning the skins or hides of high-fat content, then, while 'wet, and the fibres thereof are liquid-impregnated, subjecting the tanned skins or hides to the action of a degreasing fluid that is not miscible with the liquid and an emulsifier for producing with the liquid an emulsion for rendering the degreasing fluid miscible with the liquid,

thereby to enable the degreasing fluid to penetrate the liquid-impregnated fibres of the skins or hides, and extracting thedegreasing fluid from the fibres of the skins or hides.

5. A method of treating skins or hides of highfat content that comprises subjecting the skins or hides of high-fatcontent, prior to removing the fats thereof, to the action of a tanning S0111: tion containing an emulsifier to tan the skins or hides, and then, while wet, and the fibres thereof are liquid-impregnated, subjecting the tanned skins or hides to the action of a degreasing fluid that is not miscible with the liquid and an emulsifier for producing with the liquid an emulsion for rendering the degreasing fluid miscible with the liquid, thereby to enable the degreasing fiuid to penetrate the liquid-impregnated fibres of the skins or hides.

6. A method of treating skins or hides of highfat content that comprises subjecting the skins or hides of high-fat content, prior to removing the fats thereof, to the action of an aqueous tanning solution containing a fatty-alcohol-sulphate emulsifier to tan the skins or hides, and then subjecting the tanned skins or hides to the action tanned skins or hides to the action of a chlormated-hydrocarbon emulsified in water through the agency of a fatty alcohol sulphate to degreasethe tanned skins or hides.

9. A method of treating skins or hides of highfat content thatcomprises first tanning the skins or hides ofhigh-fat content, then, while wet, and the fibres thereof are liquid-impregnated, subjecting the tanned skins or hides to the action of trichlorethylene and an emulsifier, and extracting the trichloroethylene from the fibres of the skins or hides.

10. A method of treating skins or hides of highfat content that comprises first tanning the skins or hides of high-fat content, then, while wet, and the fibres thereof are liquid-impregnated,

subjecting the tanned skins or hides to the action of methylene chloride and an emulsifier, and extracting the methylene chlorflie from the fibres of the skinsor hides.

11. A method of treating skins or hides of high-fat content that comprises tanning the skins or hides, of high-fat content, and subjecting the tanned skins or hides while wet to the action of a chlorinated-hydrocarbon emulsion at a temperature sufficiently high to liquefy the fats in the tanned skins or hides, but not so high as to injure the skins or hides, thereby to enable the chlorinated-hydrocarbon emulsion to extract the liquefied fats in order to degrease the skins or hides.

12. A method of treating skins or hides of high-fat content that comprises tanning the skins or hides of high-fat content, and subjecting the tanned skins or hides while wet to the action of a-chlorinated-hydrocarbon emulsion at a temperature of about between F. to'140" F. to degrease the tanned skins or hides.

- 13. A method of treating skins or hides of high-fat content that comprises tanning the skins or hides of high-fat content, subjecting the tanned skins or hides while wet to the action of a chlorinated-hydrocarbon emulsion at a temperature sufficiently high to liquefy the fats in the tanned skins or hides, but not so high as to injure the skins, thereby to enable the chlorinated-hydrocarbon emulsion to extract the liquefied fats in order to degrease the skins, removing the degreased tanned skins or hides from the emulsion, and distilling the chlorinated-hydro,- carbon still remaining in the skins or hides out of the skins or hides.

14. A method of treating skins or hides of highfat content that comprises tanning the skins or hides of high-fat content, subjecting the tanned skins or hides while wet to the action of a chlorinated-hydrocarbon emulsion at a temperature sufficiently high to liquefy the fats in the tanned skins or hides, but not so high as to injure the skins or hides, thereby to enable the chlorinatedhydrocarbon emulsion to extract the liquefied fats in order to degrease the skins or hides, removing the degreased tanned skins or hides from the emulsion, and subjecting the skins or hides to the action of a vacuum to remove the chlorihated-hydrocarbon still remaining in the skins or hides.

15. A method of treating skins or hides of highfat content that comprises first tanning the skins or hides of high-fat content, then, while wet, and the fibres thereof are liquid-impregnated, subjecting the tanned skins or hides to the action of a degreasing fluid that is not miscible with the liquid and an emulsifier for producing with the liquid an emulsion for rendering the degreasins fluid miscible with the liquid, thereby to enable the degreasing fluid to penetrate the liquid-impregnated fibres of the skins or hides, and subjecting the tanned skins or hides to the action of a vacuum to extract the degreasing fluid from the fibers of the skins or hides.

16. A method of treating skins or hides of highfat content that comprises first tanning the skins or hides of high-fat content, then, while wet, and the fibres thereof are liquid-impregnated, subjecting the tanned skins or hides to the action of a degreasing fluid that is not miscible with the liquid and an emulsifier for producing with the liquid an emulsion for rendering the degreasing fluid miscible with the liquid, thereby to enable the degreasing fluid to penetrate th liquid-impregnated fibres of the skins or hides, and sub jecting the tanned skins or hides to a relatively low pressure and to a temperature sufliciently high to cause the degreasing fluid to boil out of the skins or hides but not so high as to injure the skins or hides.

17. A method of treating skins or hides of highfat content that comprises first tanning the skins or hides of high-fat content, then, while wet, and the fibres thereof are liquid-impregnated, subjecting the tanned skins or hides to the action of a degreasing fluid that is not miscible with the liquid and an emulsifier for producing with the liquid an emulsion for rendering the degreasing fluid miscible with the liquid, thereby to enable the degreasing fluid to penetrate the liquid-impregnated fibres of the skins or hides, subjecting the tanned skins or hides to a temperature 511!- flciently high to facilitate the degreasing or the skins or hides but not so high as to injure the skins or hides, and extracting the degreasing fluid from the fibres of the skins or hides while maintaining them at the said temperature.

18. A method of treating skins or hides of highfat content that comprises subjecting the skins or hides of high-fat content, prior to removing the fats thereof, to the action of a tanning solution containing an emulsifying agent to tan the skins or hides, and subjecting the tanned skins or hides to the action of a chlorinated-hydrocarbon emulsified in water through the agency or a fatty-alcohol sulphate to degrease the tanned skins or hides.

19. A method or treating skins or hides of highfat content that comprises subjecting the skins orhides of high-tat content, prior to removing the fats thereof. to the action of a tanning solution containing an emulsifying agent to tan the skins or hides, subjecting the tanned skins or hides while wet to the action of a chlorinated-hydrocarbon emulsion to degrease the tanned skins or hides, removing the degreased tanned skins or hides from the emulsion, and distilling the chlorinated-hydrocarbon still remaining in the skins or hides out of the skins or hides.

20. A method of treating skins or hides or highfat content that comprises subjecting the skins or hides oi high-fat content, prior to removing the fats thereof, to the action of a tanning sol-ution containing an emulsifying agent to tan the skins or hides, then, while wet, and the fibres thereof are liquid-impregnated, subjecting the tanned skins or hides to the action or a degreesing fluid that is not miscible with the liquid and an emulsifier for producing with the liquid an emulsion for rendering the degreasing fluid miscible with the liquid, thereby to enable the degreasing fluid to penetrate the liquid-impregnated fibres of the skins or hides, and extracting the degreasing fluid from the fibres of the skins or h es.

21. A method or treating skins or hides of highfat content that comprises subjecting the skins or-hides oi high-fat content, prior to removing the fats thereof, to the action of a tanning solution containing an emulsifying agent to ten the skins or hides, then subjecting the tanned skins or hides to the action 01, thereby to impregnate the fibres of the skins or hides with, a liquid 0 taining a degreasing fluid that is not miscgle with the liquid and an emulsifier for producing with the liquid an emulsion for rendering the degreasing fluid miscible with the liquid, thereby to enable the degree-sing fluid to penetrate the liquid-impregnated fibres of the skins or hides, maintaining the liquid at a temperature sufliciently high to facilitate the degreasing o! the skins or hides but not so high as to injure the skins or hides, separating the skins or hides from the liquid, subjecting the skins or hides to the action or a vacuum to extract the liquid re-' maining in the fibres of the skins or hides, and supplying heat to the skins or hides during the extraction.

OLIVER WILLIAM ROBERTSON. 

